1. Field of the Invention
The present invention relates to a throttle control apparatus installed on an internal combustion engine, and more particularly to a throttle control apparatus for controlling the opening and closing action of a throttle valve by a driving source such as a motor and so on in response to an operation of an accelerator and for being able to perform various controls such as a constant speed driving control and so on.
2. Description of the Prior Art
In an internal combustion engine which is provided with a carburetor, a throttle valve controls a mixed gas which air and fuel are mixed each other and in an internal combustion engine which is provided with an electronic controlled fuel injection apparatus, a throttle valve controls the generating power of the internal combustion engine by adjusting the intake air flow. These throttle valves are constituted so as to link with an accelerator operation mechanism including an accelerator.
In recent years, apparatuses which open and close the throttle valve by a driving source such as a motor and so on in response to an operation of an accelerator are proposed in contrast to the above prior art which the accelerator operation mechanism is mechanically connected with the throttle valve. An apparatus which drives a stepping motor connected with the throttle valve in response to an operation of an accelerator is disclosed, for example, in Japanese patent application laid-open publication No. 55(1980)-145867.
This apparatus includes an electromagnetic clutch interposed between a throttle shaft and a rotating shaft rotated by a depression of the accelerator and arranged so as to separate both shafts from each other in its exciting condition and to connect both shafts each other in its nonexciting condition and a control circuit for detecting abnormalities of operations of an electronic controlled actuator and for stopping the supply of an electric source to the electronic controlled actuator and the electromagnetic clutch by a relay. In this apparatus, the throttle shaft is mechanically connected with the accelerator via the electromagnetic clutch when the control of the electronic controlled actuator became impracticable.
Furthermore, an apparatus which overcomes a drawback of the prior apparatus disclosed in the above publication is disclosed in Japanese patent application laid-open publication No. 63(1988)-80039. In this apparatus, the accelerator operating portion and the throttle valve are connected each other when the amount of the throttle valve opening corresponded to the operational amount of the accelerator operating portion under the abnormal condition of the actuator and so on in contrast to the above prior apparatus which the amount of the throttle valve opening does not correspond to the operational amount of the accelerator operating portion when the accelerator operating portion and the throttle valve were connected each other. According to this apparatus, the electric current is not turned on an electromagnetic coil under the normal condition and is turned on the electromagnetic coil under the abnormal condition so as to connect the throttle valve and an accelerator link each other. And then the electric current which is turned on the electromagnetic coil is interrupted temporarily when the accelerator was released in the abnormal condition and thereby the connection between the accelerator link and a clutch disk is released. After the throttle valve has fully closed the electromagnetic coil is excited again and thereby the accelerator link and the clutch disk are connected each other.
In the above described prior throttle control apparatuses, however, the clutch mechanism is connected by a frictional engagement or an engagement between an engaged member (an engaged pin) and an engaged groove (an engaged hole). According to the former clutch mechanism using the frictional engagement, it is difficult to transmit the driving force and scaling up of the clutch mechanism and the apparatus is unavoidable in order to transmit the requisite driving force. On the other hand, according to the latter clutch mechanism using the engagement between the engaged member and the engaged groove, the transmitting portion of the driving force becomes point contact substantially as the apparatus disclosed in the above Japanese patent application laid-open publication No. 63(1988)-80039 and moreover fairish rotational angle is necessitated for obtaining the engagement between the engaged member and the engaged groove after a clutch plate contacted with a driven gear. Thereby, the wasteful rotation is caused in the motor as the driving source. In particular, when the stepping motor is applied in order to give the accurate rotation to the clutch plate, it is necessary to correct the rotation angle after the connection and a correction amount enlarges in case of the connection by the engagement between the engaged member and the engaged groove.
Furthermore, in the above described prior throttle control apparatuses, neither the clutch plate nor the driven gear connected therewith are hollow as disclosed in the above latter publication and it is difficult to form an opening portion in the clutch plate or the driven gear from positions of the clutch plate and the driven gear. Even if it is able to form the opening portion, since a distance between the outer tooth portion of the driven gear and the portion of the engaged member and the engaged groove which the driving force is transmitted is large, it is not able to form a very large opening portion and therefore it is not able to expect making light weight. Furthermore, the engaged member is not only necessitated but it is necessary to thicken the thickness of the clutch plate in order to form the engaged member. Therefore, it is necessary to take a special measure to miniaturize component parts.